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Full text of "Air delivery of water helps control brush and grass fires"

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< C No. 99 



FOREST RESEARCH NOTES 

st 

CALIFORNIA FOREST AND RANGE EXPERIMENT STATION, 

GEORGE' M JEMISON, DIRECTOR 

7 (u.s. 

U.S. DEPARTM^TpSSRgtrm«e--B 

Current seriai record 
DEC 3 1959 „ 




October 20, 1955 



3 



AIR DELIVERY OF WATER. HELPS CONTROL 
BRUSH AND GRASS FIRES 



By -Joseph B. Ely , Fire Control Officer, Mendocino National Forest, 

and Arthur W. Jensen, Forester, Division of Forest Fire Research, 
California Forest and Range Experiment Station. 



Dropping water or fir e-retardant chemicals from low-flying air- 
craft can help ground forces control brush and grass fires. That such 
water drops are practicable has been demonstrated by a recent series 
of field trials and calibration tests conducted by the Mendocino 
National Forest and the California Forest and Range Experiment 
Station in cooperation with the Willows Flying Service, the California 
Division of Forestry, and the Arcadia Equipment Development Center. 
As much as 120 gallons of water at a time was carried to fires in an 
airplane normally used for crop dusting and other agricultural purposes, 
Water dropped through a single outlet designed by the Willows Flying 
Service proved effective in quieting hot spots on large fires and in re- 
tarding spread of small fires in brush and grass, 

1 / 

Previous studies — have established several guidelines for drop- 
ping water from aircraft: 

1. The danger to men, equipment, and buildings 
prohibit the use of missiles or droppable con- 
tainers--^ fact, any projectile - -in populated 
areas or as close support to fire fighters on 
the ground. 

2. Aircraft must be maneuverable and have a 
considerable reserve of power. 

1/ See Bibliography, page 12. 

,~ The California Forest and Range Experiment Station is maintained at Berkeley in cooperation with the University of California 

**** «* 



3. Pilots should be capable of flying close to rough 
topography and of achieving pinpoint accuracy 
with safety, 

4. Water dropped free-fall reaches the ground and 
has a significant effect on some fires. 

In consideration of these guidelines, it was decided to test the adap 
tability of an agricultural aircraft as an aerial tanker, and to at- 
tempt drops of uncontained water on fires. 

THE AE RIAL TANKER 

At the suggestion of the fire-control staff of the Mendocino 
National Forest, the Willows Flying Service adapted a plane used 
in agricultural work for trial as an aerial tanker. This plane, a 
450 -hor s epower biplane (fig. 1), has a 160-gallon tank in the fuse- 
lage and is equipped with conventional valves and nozzles for 
agricultural spraying and seeding operations. The spray equip- 
ment was removed and a single outlet was installed at the base of 
the tank (fig. 2). Removing the conventional equipment and instal- 
ling the special tank outlet requires about 4 hours. 

The outlet measures 7 by 18 inches and is constructed of 
heavy sheet metal. The outlet gate is hinged at the front and has 
a rubber gasket to insure watertight seal. At first, the gate was 
equipped with a simple latch released from the cockpit, With this 
arrangement, the sudden release of water caused the plane to 
jump about 100 feet and the pilot to black out temporarily. This 
difficulty was corrected by equipping the outlet gate with a con- 
trolling lever which permitted the pilot to open the gate more 
slowly, and in all subsequent tests when full loads were dropped 
the gate was opened slowly at first. 

PRELIMINARY TRIALS 



Preliminary trials were conducted in early August 1955 
over flat ground at an airport. These trials showed that water 
could be dropped successfully from this aircraft. In the first 
trial, a load of 120 gallons of water was dropped from an eleva - - 
tion of 30 feet at an airspeed of 80 miles per hour. The water 
from this drop covered an area approximately 30 feet wide and 
285 feet long. A test fire in grass, 20 feet wide and 600 feet 
long, required three 120-gallon loads of water and 10 minutes of 
follow-up work by hand for control. 



-2- 




-3- 



FIELD TRIALS 

The next step was to try water drops on actual wildfires. 
During August the plane was used 4 times on 3 fires (table 1). In 
three trials the air tanker proved to be of considerable help to 
ground forces although in one of these it was apparent that too 
iruch was expected of a single plane. One fire was under control 
when the plane arrived so that the water drop was unnecessary 
though helpful in mop=up. 

On initial attack the loaded plane was dispatched from its 
vVillows base immediately after ground forces were started to the 
fire. At the same time, aviation gasoline and a water tanker were 
sent to the airport nearest the fire. Prominent, well known peaks 
were used as landmarks, A reconnaissance plane, in communica- 
tion with ground forces and the "refill" airport, correlated the 
ground and air activity. In the future the company plans to fly a 
maintenance mechanic to the airport to refuel and load the air 
tanker, do maintenance work as necessary, and prevent damage 
to the plane by well intentioned but inexperienced personnel during 
the loading operations. 

CALIBRATION TESTS 

It was apparent that air delivery of water made this aircraft 
a practical fire fighting tool, but quantitative information was needed 
to improve tactical methods for water delivery. Accordingly, a 
limited series of tests was conducted at the vVillows airport and Elk 
Creek Butte Lookout on August 31 and September 1, 1955 to obtain 
the following information: 

1. The effect of plane height, plane speed, and 
wind velocity and direction on the amount and 
distribution of water received on the ground. 

2. The amount of water loss to be expected dur- 
ing summer fire weather. 

3. The effect on amount and distribution of drop- 
ping part of the total load in each of several 
runs (multiple passes) with the pilot aiming 
for the same spot each time. 

4. The practicability of dropping a sodium-calcium 
borate fire -r etardant from this aircraft. 



-4- 



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5. The amount of penetration of water and retar- 
dant into brush cover. 

Procedur e 

For measuring the amount and distribution of water, 121 cans, 
3 inches in diameter and 7/8 inches tall, were placed in a 50 by 300- 
foot rectangular grid. Within this grid the cans were spaced 5 feet 
apart across the width and 30 feet apart along the length. The cans 
were covered immediately after each test and the water received by 
each was weighed before making the next test. To measure penetra- 
tion into brush, 10 pairs of cans were distributed in brush of different 
densities in the target area. Each pair consisted of one can at the top 
of brush crown, and one on the ground. 

vVind direction and velocity were recorded automatically during 
each test. Temperature and relative humidity were measured imme- 
diately after each test. The line of flight of the plane with reference 
to the grid was also recorded. 

Although this aircraft can carry a maximum of 160 gallons of 
water, nominal full-load tests were made with 125 gallons of water 
or 100 gallons of retardant. At elevations normally experienced on 
the Mendocino National Forest this is the maximum safe load. 

Results 



During the tests wind velocity varied from calm to 8 miles per 
hour, air temperature from 80 to il0°F, and relative humidity from 6 
to 1 9 percent. In one test the plane's tail was low and the propeller 
wash blew over some of the grid measuring cans. 

The patterns of distribution from these tests were roughly oval, 
from 4 to 7 times longer that wide (fig. 3). When the full load was re- 
leased in one pass the greatest concentration of water was obtained 
when the airplane was flying at low speed and low elevation into the 
wind (tables 2 and 3). Both higher speed and greater elevation in- 
creased the total length of pattern but gave lower concentration. 

About 75 percent of the water reached the ground in measurable 
quantities in the low-altitude, low -speed, headwind tests; about 65 per- 
cent in the higher altitude, crosswind tests. At top speed and low ele- 
vation, about 70 percent of the water released reached the ground. Only 




Figure 3. 



--Sample distribution patterns from water-drop tests; 
contour lines indicate concentration of water in 
gallons per 100 square feet. 



Table 2. -- Length of water pattern along line ^ 
of flight, by concentration of water—' 













Amount 






Length when concentration (in gal. 




Aircraft 


Wind 


ox 






1 


jer 100 ^ 


q. ft. ) was - - 




rest 










Water 


iNO . OI 


1 Otai 












No. 


Height 


Speed 


Direction 


Velocity 


dropped 


Pas se s 


Length 


0. 5 


1. 


2.0 


3. 


4. 




Feet 


M. p.h. 




M. p. h. 


Gallons 




Feet 


Feet 


Feet 


Feet 


Feet 


Feet 


2 


30 


80 


Head 


3-5 


125 


1 


230 


210 


(2/> 


(2/) 


(2/) 


(2/) 


10 


30 


80 


Head 


6-8 


125 


1 


240 


212 


160 


100 


30 


15 


4 


30 


90 


Head 


0-2 


125 


1 


360 


305 


210 


85 


10 





3 


30 


90 


Cross 


0-1 


125 


1 


330 


280 


160 


50 








5 


90 


80 


Cross 


3-4 


125 


1 


290 


230 


100 


20 








6 


90 


80 


Cross 


4-5 


125 


1 


290 


175 


135 


10 








7 


30 


80 


Cross 


1 -4 


125 


3 


285 


210 


185 











8 


30 


80 


Cross 


2-4 


125 


5 


345 


219 


165 


20 








9 


30 


80 


Head 


0-1/2 


40 


1 


210 


175 


113 


30 








11 


30 


80 


Head 


6-8 


3/ 4 


1 


165 


(2/) 


(2/) 


(2/) 


(2/) 


(2/) 



1/ Concentration measured along 5-foot strip parallel to fight line through area of greatest 

concentration. 
2/ Collecting devices failed. 
3/ Fire retardant chemical dropped. 



Table 3. --Water distribution by area for different concentrations 













Amount 






Area 


covered by concentration 




Aircraft 


Wind 


of 






(in g 


al.per 100 sq.ft 


. ) of-- 




Test 










Water 


No. of 


Total 












No. 


Height 


Speed 


Direction 


Velocity 


dropped 


Passes 


Area 


0. 5 


1. 


2. 


3. 


4. 




Feet 


M. p. h. 




M. p. h. 


Gallons 




Sq. Ft. 


Sq. Ft. 


Sq. Ft. 


Sq. Ft. Sq. Ft. 


Sq. Ft. 


2 


30 


80 


Head 


3-5 


125 


1 


9, 613 


(2/) 


(2/) 


(2/) 


(2/) 


(2/) 


10 


30 


80 


Head 


6-8 


125 


1 


11, 332 


5, 644 


4, 000 


1, 656 


269 


26 


4 


30 


90 


Head 


0-2 


125 


1 


16, 560 


6, 375 


4, 284 


356 


19 





3 


30 


90 


Cross 


0-1 


125 


1 


14, 361 


6, 624 


3, 286 


277 








5 


90 


80 


Cross 


3-4 


125 


1 


15, 974 


6, 943 


3, 531 


75 








6 


90 


80 


Cross 


4-5 


125 


1 


15, 449 


6, 1 18 


2, 668 


112 








7 


30 


80 


Cross 


1 -4 


125 


3 


12, 818 


6, 634 


2, 902 











8 


30 


80 


Cros s 


2-4 


125 


5 


13, 350 


4, 544 


2, 607 


94 








9 


30 


80 


Head 


0-1/2 


40 


1 


7, 275 


3, 038 


1, 569 


150 









1/ Test 11 not included because measuring device failed. 
2/ Measuring device failed. 



-8- 



20 to 30 percent of the water reaching the ground was in concentra- 
tions of i gallon or more per 100 square feet. Apparently, wind 
direction and velocity is the most important factor affecting percent 
of water reaching the ground in a useful pattern. 

Relatively high concentration was obtained when a 40-gallon 
load was dropped in 1 pass as compared with a 1 25 -gallon load 
dropped in multiple passes. In making more than one pass with a 
capacity load, the manually operated outlet gate was only partially 
opened for each pass because it could not be closed against a full- 
str earn discharge. As a result, only about half of the water reached 
the ground in measurable quantity. More rapid release of water 
should result in greater concentrations for all sizes of loads. 

In medium and light brush there was no significant difference 
between the amounts of water received at the crown and on the 
ground. In heavy brush, however, there was considerable varia- 
tion from 20 to 90 percent as much water reaching the ground 
as was received at crown level. 

Results from the retardant tests were similar to those ob- 
tained with plain water. However, the heavy sodium-calcium borate 
suspension, weighing 10 pounds per gallon, did not disperse as 
readily as water (fig. 4) and had a smaller distribution pattern 
(table 2) with particularly heavy concentration in the center. All 
of the measuring cans in the center of the pattern were tipped over 
by the retardant. Penetration into heavy brush was more uniform 
than with water; 45 to 60 percent of the amount received at the crown 
level reached the ground. The standing brush was well coated with 
r etardant. 



CONCLUSIONS- AND RECOMMENDATIONS 



These limited tests have shown that water or chemical dropped 
free-fall from small airplanes can have significant effect on small 
grass and brush fires, or on some parts of large ones. To obtain 
the greatest concentration of liquid on the ground, the airplane should 
fly as low and as slowly as conditions permit and as nearly into the 
wind as possible. The more rapidly water is released, the greater 
the concentration will be. Increasing the altitude or airspeed or drop- 
ping in a crosswind will give greater area coverage but will reduce 
concentration. 

As with all specialized tools, the aircraft used for aerial tan- 
kers must be in top mechanical condition. Also, pilots must be 



A 





-1"0- 



experienced both in flying under mountain conditions and in low level 
air drops. Pilots are cautioned to watch for sudden jumps when re- 
leasing large amounts of water. They should avoid a taildown plane 
attitude when dropping from low heights to minimize effects of slip- 
stream on the water. 

One aerial tanker has been of significant assistance to ground 
crews on fires. Indications are that several planes used in quick 
succession will not only be more efficient but may be able to hold 
temporarily short pieces of hot fire line. It is not necessary to evac- 
uate the target area as uncontained water drops from this aircraft are 
not dangerous to personnel. 

Considerable work still needs to be done before the aerial tan- 
ker can become a common fire fighting tool. The optimum speed, 
altitude, direction of flight, and method of releasing the water or 
chemical for each tactical situation need to be determined. Informa- 
tion is needed on the amount of water or chemical required to affect 
fires under different fuel and burning conditions. More test drops 
should be made under a greater variety of weather and fuel conditions, 
particular ly at wind velocities greater than those encountered in these 
tests. A means of closing the outlet gate against a full stream of water 
is needed to permit higher concentrations of water than are now possible 
in multiple -pas s drops. Ground-to-air communication should be im- 
proved for better tactical use. 



-1 1 - 



BIB LICGRAPHY 



Anonymous . 

1 955. Aerial fire fighting --bulk water drop by fired wing 

aircraft. (U.S. Forest Service, San Francisco, 
California) Firestop Progress Report No. 13 pp., 
illus . 

Bor rows, J. S. 

1947 Aerial bombing of forest fires Western Forestry 

and Conservation Assoc. Proc. thirty-eighth 
annual meeting pp. Z0-Z1. 

Ellwood, B. L. 

1948. Notes on the suppression of bushfires from air- 

craft. Australian Forestry XI 1 (2 ): 1 27 - 1 33 illus. 

Mackey, T. E. 

1954. Aerial water bombing. Fireman 2i(3):19-20. 

Los Angeles County Fire Department and Others, 

1953. Aerial delivery of water equipment. 3 pp. and 
appendix illus . (Processed). 

California Division of Forestry. 

1954. El Toro Air Drop. 2pp. (Office report, District 6) 



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